1. Field of the Invention
The present invention relates to a flexible pipe for a wide range of use, e.g., as water supply and drainage pipes for roads, railways and reclaimed land, water supply and waste water drainage pipes for plant premises, various air supply and discharge pipes, underground electric wire protective pipes, other protective pipes for various purposes, and underground pressure resistant pipes. More particularly the invention relates to a flexible pipe composed of a girdling corrugation, roughly S-shaped in transverse cross section, made of rigid material, helically wound and firmly fixed onto the outer wall surface of an inner flexible pipe. Each corrugation girdle has parallel bent ends pointed opposite to each other. An integrated body is formed by consecutively engaging the adjoining bent ends of the corrugations thus would thereon which are movable in the axial direction of the flexible pipe.
2. Background of the Invention
A coventional flexible pipe of the sort described above consists as shown in FIG. 8, of a corrugation 2' prepared from rigid metal material. The two ends 2a' of each corrugation 2 are perpendicularly bent in transverse cross section. Moreover, the corrugation 2' are wound onto the wall surface (inner wall surface in this case) of a flexible pipe 1' made of flexible material. The adjoining bent ends 2a' of the corrugations 2' thus wound and anchored together are movably engaged in the axial direction of the flexible pipe so that the pipe as a whole becomes flexible.
Further, the same inventor has filed U.S. patent application Ser. No. 944,067 entitled "Flexible Hard Pipe" on Dec. 20, 1986.
In the aforesaid conventional flexible pipe, both ends 2a' of the corrugation are perpendicularly bent and the direction in which the ends thereof are bent conforms to the diametric direction of the flexible pipe 1' after the corrugations 2' are wound onto the wall surface of the flexible pipe 1' into a flexible pipe. When great bending stress is applied to the flexible pipe, the bent ends 2a' are therefore caused to move in the diametric direction of the pipe and both the ends 2a' engaged with each other tend to easily disengage. The problem is that such a flexible pipe can crack.
Although an attempt has been made to solve the aforesaid problem by spirally inserting a cord or the like in between the two bent ends 2a' engaged with each other, that problem is still left unsolved.